In the field of rubber industry, automobile components are desired to have advanced function and performance. Rubber products for use for such automobile components include power transmission belts and they are widely used, for example, for power transmission of auxiliary drive of automobile air compressors, alternators, etc. In recent years, a severe requirement for silencing is increasing, and in particular, in automobile driving devices, any other sound than engine sound is regarded as a noise, and therefore, a countermeasure to noise generation in belts is demanded.
For example, Patent Document 1 (JP-A 2003-202055) discloses a V-ribbed belt containing ribs each extending in the belt length direction on the lower surface of the belt body, in which each rib contains cotton short fibers and intermediate short fibers having an intermediate elastic modulus between the elastic modulus of the main rubber constituting the ribs and the elastic modulus of the cotton short fibers (see Claim 1, paragraph [0009]).
This document describes that the cotton short fibers smooth the change in the friction coefficient accompanied by the transition from the dampened state in absorption of water to a dry state, and that the ribs have a friction coefficient of three or more types including the cotton short fibers, the intermediate short fibers and the main rubber, thereby preventing any drastic stick-slip phenomenon, preventing repetition of slip and adhesion, and preventing noise generation.
However, for preventing the slip phenomenon and the noise generation by the action of the cotton short fibers, the intermediate short fibers and the main rubber, these short fibers must be exposed out of the surface of each rib. For exposing the short fibers out of the surface of each rib, it is necessary to form the ribs by forming an unvulcanized compressive layer, in which the short fibers are kept aligned in the belt width direction, vulcanizing it, and then cutting (grinding) the compressive layer.
Consequently, the production cost for V-ribbed belts increases, and the loss of the rubber material to be caused by cutting brings about another problem.
Given the situation, for reducing the production cost and the loss of the rubber material for such V-ribbed belts, for example, Patent Document 2 (JP-A 2008-281153) discloses a V-ribbed belt in which the plural ribs each extending in the belt length direction on the inner peripheral part thereof comprise unground rubber, the surfaces (frictional power transmission surfaces) of the ribs that are in contact with pulleys have, as flocking to stand thereon, short fibers (flocking yarns) to form a surface fibrous layer, and further, inside the ribs, formed is a flocking rubber layer with the short fibers kept embedded therein, and the thickness of the flocking rubber layer falls within a range of from 35 to 200 μm from the rib surface; and a production method for the same (see claims, paragraphs [0011] and [0023], and Examples). As a method for forming the flocking rubber layer, in this document, a liquid adhesive is applied by means of a spraying method or a dipping method, and short fibers (polyamide, etc.) having a pile length of from 0.1 to 5 mm are electrostatically planted to flock.
This V-ribbed belt is produced as follows. An extensible layer, a tension member, a compressive layer, an adhesive layer (layer of liquid adhesive), and a flocking layer are laminated in this order on an inner mold to form an unvulcanized belt sleeve, then the unvulcanized belt sleeve is pressed against an outer mold having, on the inner side thereof, a rib marking from the inner peripheral side thereof and vulcanized in that condition to produce a rib-marked vulcanized belt sleeve, and the vulcanized belt sleeve is cut into a desired width. According to this production method, the V-ribbed belt may have ribs formed thereon without grinding, and can therefore solve the above-mentioned problem. In addition, this document describes that, in the V-ribbed belt, the surface fibrous layer formed on the frictional power transmission surface thereof prevents noise generation in the initial stage of driving, and the flocking rubber layer formed inside the ribs can prevent noise generation since the short fibers can stay inside the compressive rubber layer even after the belt has run for a long period of time.
However, in adhesive application before flocking in the belt production, the liquid adhesive is applied extremely thinly, and therefore, in forming the rib by pressing the unvulcanized belt sleeve against the rib mark on the outer mold, the compressive rubber layer that has been softened by heating to be in a flowable state would take many flocked short fibers inside it and, as a result, sufficient short fibers could not exist on the surface to be in contact with pulleys (especially near the center part around the rib side surfaces), therefore providing a risk of noise generation in the initial stage.
Patent Document 3 (JP-A 2010-101489) discloses a transmission belt having elastomer teeth of an ethylene-α-olefin elastomer each covered with a barrier layer of a thermoplastic material, in which the barrier layer is covered with an outer cover formed of a woven or nonwoven fabric and the outer side cover on at least the flank of the elastomer teeth is partially included in a part of the thickness of the barrier layer (see claims, and paragraphs [0037], [0039], [0040] and [0051]). This documents describes that the barrier layer prevents the teeth rubber (source material constituting the elastomer teeth) from passing through the cover during belt formation and the cover (fibers or yarns) is partially embedded inside a part of the thickness of the barrier layer to thereby improve the cracking resistance of the barrier layer and, in addition, the remaining part of the cover not embedded is protruded out (exposed out) on the side of pulleys to thereby prevent noise generation. Further, it is disclosed that the barrier layer and the cover are previously integrated through calendering and rolling, and the nonwoven fabric penetrates into the film only partially and can be therefore absolutely prevented from penetrating into the teeth rubber that changes from the raw (unvulcanized) state to a vulcanized state. In addition, the document further discloses that, as the woven or nonwoven fabric to form the cover, especially suitable is a polyethylene-based woven or nonwoven fabric.
However, in this drive belt, the cover is merely embedded only partially inside a part of the thickness of the barrier layer, and with the progress of abrasion along with belt running, only the barrier layer with no cover thereon is to be soon exposed out, and therefore there is also a risk of reduction in the cracking resistance and the abrasion resistance of the barrier layer. In that situation, in addition, since the barrier layer is not reinforced with a cover, the barrier layer would peel off from the surface of the elastomer teeth due to shearing from pulleys or there may be a probability that the barrier layer would break in the inside thereof. Further, though the drive belt uses a peroxide for curing the teeth rubber or any other chemical having curability to thereby promote the bonding between the teeth and the barrier layer, it could not be said that only the chemical action would be sufficient for preventing the barrier layer from peeling off and, in addition, it could not be effective against the destruction inside the barrier layer.